1. Field of the Invention
The present invention relates to digital oscilloscopes and to engine analyzers incorporating digital oscilloscope displays. The invention has particular application to cursor control on the display screen of such an oscilloscope.
2. Description of the Prior Art
It is known to provide digital oscilloscopes with multiple display traces (e.g. two), so that a number of waveforms can be simultaneously displayed. A dual-trace scope can typically be operated in either single-trace or dual-trace mode. It is also known to provide engine analyzers with display screens which essentially constitute digital oscilloscopes. Such analyzers acquire analog waveforms from an associated engine by means of pickup leads and then digitize the data for storage in memory and display on the digital oscilloscope screen.
The horizontal scale (also called sweep) of an oscilloscope represents time. Broadly speaking, in a digital engine analyzer scope there are two types of sweeps: engine sweeps and fixed-time sweeps. Engine sweeps display a waveform for either a single cylinder ignition or for a complete engine cycle (the time between consecutive firings of the same cylinder), and are typically used to display waveforms related to cylinder ignition events. Engine sweeps may typically be of any of three different types: cylinder, parade and raster. Since engine sweeps begin and end with the firing of a cylinder, the time represented by an engine sweep varies with engine speed. Fixed-time sweeps, e.g., 10 ms, 100 ms, etc.) display a fixed period of time across the width of the display screen and are typically used to display waveforms other than primary and secondary ignition waveforms.
It is known to provide for each trace of the oscilloscope one or more cursors which are movable relative to the waveform to facilitate measurements with respect to the waveform. More particularly, each cursor can be arranged to intersect the waveform and there may be provided an indicator to denote the value of the waveform at the point of intersection with the cursor. The cursors can be moved relative to the waveform to effect different measurements.
In a dual-trace digital scope, the cursor movements for the two traces are synchronized. Thus, the cursors for one trace are, respectively, vertically aligned with the cursors for the other trace and, if a cursor in one trace is moved, the corresponding cursor in the other trace is moved in the same manner. This synchronization limits the utility of the cursors.